std::chrono...::operator-=(3)

💅 NAME 💅

okay so this is the std::chrono...::operator-=(3) page from the C++ Standard Libary manual — and yes, the header really spells it Libary, and I'm not fixing it, bestie 💀. The NAME line is std::chrono::month::operator+=,std::chrono::month::operator-=, then a dash, then the exact same thing again: std::chrono::month::operator+=,std::chrono::month::operator-=. slay.

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✨ Synopsis ✨

The page lists two signatures, both constexpr, both returning std::chrono::month&, both taking const std::chrono::months& m, and both noexcept. They're giving since-C++20 energy.

• (1) (since C++20)

constexpr std::chrono::month& operator+=( const
std::chrono::months& m ) noexcept;

• (2) (since C++20)

constexpr std::chrono::month& operator-=( const
std::chrono::months& m ) noexcept;

Adds or subtracts m.count() from the month value, reducing the result modulo 12 to an integer in the range [1, 12].

• 1) Performs *this = *this + m;.
• 2) Performs *this = *this - m;.

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🫶 Return value 🫶

A reference to this month after modification.

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🌸 Notes 🌸

After a call to one of these functions, ok() is always true if no overflow occurred during the operation.

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🎀 Example 🎀

the page says // Run this code before the snippet, so here's that exact code:

#include <chrono>
#include <iostream>

int main()
{
    std::cout << std::boolalpha;

    std::chrono::month m{6};
    m += std::chrono::months(2);
    std::cout << (m == std::chrono::month(8)) << ' '
              << (m == std::chrono::August) << ' ';

    m -= std::chrono::months(3);
    std::cout << (m == std::chrono::month(5)) << ' '
              << (m == std::chrono::May) << ' ';

    m = std::chrono::October;
    m += std::chrono::months{8}; // ((10 += 8 == 18) % 12) == 6;
    std::cout << (m == std::chrono::June) << ' ';

    m -= std::chrono::months{std::chrono::December -
       std::chrono::February}; // -= 10
    // (6 -= 10) == -4; -4 % 12 == (12 - 4) == 8
    std::cout << (m == std::chrono::August) << '\n';
}

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🍓 Output 🍓

true true true true true true

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👑 See also 👑

the See also crew:

• operator++
• operator++(int) — increments or decrements the month
• operator-- — (public member function)
• operator--(int)
• operator+ — performs arithmetic on months
• operator- — (function)
• (C++20)

that's the whole page, mwah 💋 — source/version http://cppreference.com, date 2024.06.10, and the footer's page name std::chrono...::operator-=(3).